1. Field of the Invention
This invention relates to the turbine casing structure of a turbine, such as a gas turbine or a steam turbine.
2. Description of the Related Art
With a turbine such as an industrial gas turbine or steam turbine of a large size, its interior is at a high temperature. Thus, a temperature difference between its interior and its exterior exerts a great influence. As a result, thermal deformation of the stationary portion occurs, causing oval deformation, etc. and thus necessitating a larger gap between the stationary side (stationary blades assembled to an inner casing to be described later) and the rotating side (moving blades assembled to a rotor). To diminish the thermal influence, use is made of a structure of a turbine casing in whose interior a casing (inner casing) is further provided (namely, a double-casing structure). This structure has a single air layer provided between a gas channel portion, through which a high temperature gas flows, and the air outside the turbine casing.
The inner casing has a structure supporting the blades on the stationary side, and the inner casing is supported by and fixed to an outer casing.
An example of a turbine having such a structure is a turbine having a turbine casing structure 30 as shown in FIG. 10. With the turbine casing structure 30, supporting and positioning (alignment adjustment) of an inner casing (blade ring) 32 with respect to an outer casing 31 are performed by torque pins 33 in a right-and-left direction (lateral direction), and by horizontal keys 34 in an up-and-down direction (vertical direction), respectively, when viewed from the upstream side of the turbine. As shown in FIG. 11, the horizontal key 34 is fixed to a parting surface 32b of a lower-half inner casing 32a by a bolt 35, and has a front end portion 34a installed between an upper liner 36 and a lower liner 37 provided in the vicinity of a parting surface 31a of the outer casing 31.
Another example of a turbine having the aforementioned double-casing structure is a turbine having a positioning mechanism for a turbine casing as described in Japanese Patent Application Laid-Open No. 2004-162536 (hereinafter referred to as Patent Document 1). With this turbine casing positioning mechanism, an eccentric pin is inserted into an adjusting hole formed in an engine casing (outer casing) A trunk portion of the eccentric pin is disposed in the adjusting hole, while a front end portion of the eccentric pin eccentric with respect to the trunk portion is disposed in an adjusting groove formed in the turbine casing (inner casing) while extending in an axial direction. A parallel pin is mounted to whirl-stop the eccentric pin with respect to the adjusting hole, and the eccentric pin is fixed to the engine casing by a cover body disposed in contact with the head of the eccentric pin.
Japanese Patent Application Laid-Open No. 2001-107922 (hereinafter referred to as Patent Document 2) discloses a flangeless casing fastening structure for fastening upper and lower casings. With the flangeless casing fastening structure, bolt holes are formed in the upper and lower casings, and a cylindrical sleeve is mounted by screwing an outside screw, which is formed in an outer periphery thereof, into a tapped hole provided in the vicinity of a joining surface at the bolt hole of the upper casing. A large-diameter portion to be joined to an upper end surface of the sleeve when a bolt is fastened into the bolt hole of the lower casing is formed in the bolt, and the bolts are inserted into the bolt holes to fix the upper and lower casings.
Japanese Patent Application Laid-Open No. 1997-112204 (Patent Document 3) discloses an upper-lower bolt tightening structure for coupling type 180°-divided stationary blades which fixes a stationary blade ring to a turbine casing. With the upper-lower bolt tightening structure for coupling type 180°-divided stationary blades, upper and lower stationary blades are integrated by bolts with holes, and keys fixed in the holes of the bolts with the holes are disposed between upper and lower liners provided in the turbine casing to fix the stationary blade ring to the turbine casing.
With the aforementioned turbine casing structure 30, an improvement in the accuracy of setting a clearance between the rotating side and the stationary side has been desired in recent years from the aspects of improved performance and reliability. Thus, after the inner casing 32 is mounted in the outer casing 31, the clearance between the inner casing 32 and the outer casing 31 is measured. If the measured value is not within the tolerance of the design value, the inner casing 32 is taken out of the outer casing 31, and the horizontal keys 34 are machined to optimize the clearance. Using the machined horizontal keys 34, the inner casing 32 is assembled again into the outer casing 31. With the conventional turbine casing structure 30, therefore, the position in the up-and-down direction (vertical direction) of the inner casing 32 with respect to the outer casing 31 cannot be adjusted from the outside. This poses the problem of impairing the efficiency of an adjusting operation, thereby increasing the cost of the operation.
With the turbine casing positioning mechanism described in Patent Document 1, the positioning mechanisms are disposed at upper and lower portions of the engine casing and the turbine casing, whereby the position in the right-and-left direction of the turbine casing with respect to the engine casing is restrained by the upper portion and the lower portion thereof. Thus, even if the turbine casing is thermally expanded, its central position is not displaced in the right-and-left direction with respect to the engine casing, and the concentric relationship between the engine casing and the turbine casing can be maintained. Even with the use of this positioning mechanism, however, the position in the up-and-down direction of the turbine casing with respect to the engine casing cannot be adjusted. Even if the positioning mechanisms are disposed in the vicinity of the parting surfaces of the engine casing and the turbine casing, the position in the up-and-down direction of the turbine casing with respect to the engine casing cannot be adjusted. With the turbine casing positioning mechanism, therefore, like the turbine casing structure 30, the optimal adjustment of the clearance between the engine casing and the turbine casing requires that the turbine casing be taken out of the engine casing, and the positioning mechanism and the positioning mechanism for the vertical position be machined for adjustment. This poses the problem that the position in the up-and-down direction of the turbine casing with respect to the engine casing cannot be adjusted from the outside.
With the flangeless casing fastening structure described in Patent Document 2, the inner casings or the outer casings divided into upper and lower portions can be coupled. However, the problem arises that the position in the up-and-down direction of the inner casing with respect to the outer casing cannot be adjusted from the outside.
With the upper-lower bolt tightening structure for coupling type 180°-divided stationary blades described in Patent Document 3, the keys fixed to the hole-formed bolts coupling the upper-half and lower-half stationary blades are disposed between the upper and lower liners provided in the turbine casing. By so doing, the inner casing can be locked at a predetermined position with respect to the outer casing. However, the adjustment of the position in the up-and-down direction of the inner casing with respect to the outer casing requires machining of the keys. This presents the problem that the position in the up-and-down direction of the inner casing with respect to the outer casing cannot be adjusted from the outside.
The present invention has been accomplished in light of the above-described problems. It is an object of the invention to provide a turbine casing structure in which the position in the up-and-down direction of the inner casing with respect to the outer casing can be adjusted from the outside.